This application claims priority to Japanese Patent Application Serial Number 2001-313094, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to methods and apparatus for manufacturing a press formed article from a sheet material. More particularly, the present invention relates to methods and apparatus for manufacturing a press formed article, e.g., a ring gear, from a disk-like sheet metal.
2. Description of the Related Art
A method for manufacturing a press formed article is taught, for example, by Japanese Laid-open Patent Publication Number 9-248646, in which a ring gear is exemplified as a press formed article that can be prepared utilizing the known method. In this known art, a sheet material is clamped between upper and lower dies of a first press forming machine. Thereafter, a punch associated with the upper die is lowered toward a corresponding die opening defined within the lower die, so as to stamp out an intermediate ring gear (i.e., an intermediate product). At the same time, gear teeth are formed around the outer periphery of the intermediate ring gear. However, burrs or fins are also formed around the intermediate ring gear and the burrs or fins project along the stamping direction. In addition, each of the gear teeth of the intermediate ring gear may have a dull upper edge or shear drop due to shearing. Therefore, the intermediate ring gear is reversed or turned over and is clamped between upper and lower dies of a second press forming machine or reshaping machine. Thereafter, a punch associated with the upper die is lowered toward a corresponding die opening defined within the lower die such that the intermediate ring gear is reversibly squeezed or reshaped, to thereby form the ring gear (i.e., the final product) having a desired shape and size.
According to this known method, when the intermediate ring gear is squeezed, the burrs may be compressed and partially move into the gear teeth as a result of plastic flow caused by plastic deformation. As a result, the burrs may effectively be removed. At the same time, the shear drop of the teeth may be reshaped and raised.
However, the teeth shear drop once produced typically can not be sufficiently or completely reshaped and raised using the known method due to reduced plastic flow characteristics or low plastic deformability of the material. Such insufficient raising of the teeth shear drop may result in an inferior quality ring gear.
It is, accordingly, one object of the present teachings to provide improved methods and apparatus for manufacturing a press formed article.
In one embodiment of the present teachings, methods are taught for manufacturing a press formed article. For example, a substantially flat material may be half die cut by press forming, to thereby form a first processed material having a first intermediate press formed article defined therein. The half die cutting step may be performed while compressing the central portion of the material in order to cause or induce outward plastic flow within the first intermediate press formed article. Optionally, the first intermediate press formed article may be pressed back into the first processed material, to thereby form a second processed material having a second intermediate press formed article. Further, the second intermediate press formed article may be pushed off or separated from the second processed material, to thereby form a final processed material and an unfinished press formed article.
In another embodiment of the present teachings, the unfinished press formed article may be subsequently stamped in order to form an opening therein.
According to the present teachings, when the first intermediate press formed article is half die cut, the peripheral edge of the first intermediate press formed article may simultaneously be raised due to the plastic flow caused by plastic deformation of the material. Therefore, dull edges or shear drops are not substantially produced in the first intermediate press formed article. Consequently, it is not necessary to reform the first intermediate press formed article and it is possible to efficiently increase the quality of the press formed article.
Other objects, features and advantage of the present invention will be ready understood after reading the following detailed description together with the accompanying drawings and the claims.